The present invention relates to an actuator apparatus including a marker device.
Mechanical actuators are known which use a closed loop control system wherein a position sensor provides a signal indicative of a position of a component being moved by the actuator. For example, in some aerospace applications, such mechanical actuators, powered by electric motors, are used to move nozzles. In an ideal situation the position sensor would be sited at, or close to, the nozzle so that load induced deformations (e.g. bending) of the mechanical components of the actuator would not affect the sensed position. In practice, a hostile environment (high temperatures, vibration etc.) in the vicinity of the nozzle means that it is not practical to locate the position sensor at, or close to, the nozzle. Therefore, the position sensor is located on a component of the motor or actuator remote from the nozzle.
However, problems may arise if the stiffness of actuator components is reduced, which is desirable for saving weight and production costs. It has been found that the force required to move a nozzle can be large enough to cause a significant elastic deformation of the actuator, resulting in an error in the indicated position of the nozzle.
In accordance with the invention, there is provided an actuator apparatus comprising an actuator member, an actuated element movable by actuation of said actuator member, and a marker device including a marker the position of which can be sensed in use by sensor means, said marker device being secured to said actuator member such that deformation of the actuator member during actuation to move said element causes an adjustment to the change in position of the marker.
Such apparatus facilitates more accurate estimation of the position of the actuated element.
Preferably, the actuator member comprises an actuator arm having a longitudinal axis, the marker device being secured to the actuator member such that deformation of the actuator arm causes a displacement of the marker device laterally of the longitudinal axis of the actuator arm.
Preferably, the actuator apparatus includes sensor means for sensing the change in position of the marker.
The sensor means may include indicator means for providing an indication of a change of position of said marker.
Desirably said marker device is secured to said actuator member such that said adjustment to the change in position of the marker compensates for the deformation of the actuator member and also for deformation of other members of the apparatus.
Such an arrangement of the marker device gives rise to position indication based on an apparent high stiffness of the actuator components, so facilitating the use of less stiff actuator components resulting in lighter weight components and lower material costs, whilst providing an accurate indication of the position of the actuated element.
Conveniently, the sensor means comprises a potentiometer and the marker is drivingly connected to a wiper of the potentiometer.